Derivative Financial Instruments - Derivative Netting (Details) $ in Millions	Sep. 30, 2019 USD ($) party	Dec. 31, 2018 USD ($) party
Credit Derivatives
Number of counter-parties (party) | party	6	4
Notional amount	$ 317	$ 306
Credit exposure	14	9
Exposure, net of collateral	$ 1	$ 1
A plus
Credit Derivatives
Number of counter-parties (party) | party	5	3
Notional amount	$ 276	$ 283
Credit exposure	13	9
Exposure, net of collateral	$ 1	$ 1
A
Credit Derivatives
Number of counter-parties (party) | party	1	1
Notional amount	$ 41	$ 23
Credit exposure	1	0
Exposure, net of collateral	$ 0	$ 0